JP2008108862A - Capacitor element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enlarge a band which a capacitor can use. <P>SOLUTION: In the capacitor having a pair of electrodes and a dielectric sandwiched between a pair of the electrodes, a frequency with which orientation polarization of the dielectric dissipates is set to be lower than a self-resonance frequency of the capacitor. In the dielectric having a characteristic in a figure, dielectric relaxation occurs near 10<SP>9</SP>Hz, for example. When the dielectric is to be used, the self-resonance frequency is set to become 10<SP>9</SP>Hz or above. To put it concretely, relaxation time is adjusted on the dielectric, and the capacitor is formed by using the dielectric. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a capacitor element and a method of manufacturing the same, and more particularly to a capacitor element having improved high-frequency characteristics using dielectric relaxation of a dielectric and a method of manufacturing the same.

With the development of technology in recent years, the operating frequency of devices has increased. Accordingly, capacitor elements used in equipment are also required to support high frequencies.
In general, a capacitor is represented by an equivalent circuit shown in FIG. As shown in the drawing, the capacitor has an equivalent series resistance ESR (Ω) and a parasitic inductance L (H) as parasitic elements in addition to the original capacitance C (F). Therefore, the impedance Z _C (Ω) of the capacitor is given by equation (1).

ただし、jは虚数単位、ωは角周波数(rad/s)である。角周波数ωは周波数ｆ(Hz)の２π倍（ω＝2πf）。
ここで、キャパシタンスCの含まれる１/ｊωCの項は、用いられる周波数（角周波数ω）が上昇すればするほど、小さくなっていく。逆に、寄生インダクタンスLが含まれる項ｊωLは、周波数が上昇すればするほど大きくなっていく。そのため、周波数が低く、ωL＜１/ωCとなるときには、キャパシタンスCに関する項が大きいため、キャパシタンスCの影響の方が大きい。したがって、キャパシタンスCの動作、つまり、コンデンサとして動作する。しかし、周波数が上昇すると、キャパシタンスの項１/ｊωCに比べ、寄生インダクタンスの項ｊωLが大きくなる。したがって、キャパシタンスの影響より寄生インダクタンスの影響の方が大きくなるため、コンデンサとして動作しなくなる。また、ｊωL＝−１/ｊωＣとなれば、キャパシタンスCと寄生インダクタンスが打ち消しあう。この周波数のときに、インピーダンスZ_Cは最小となり、キャパシタンスCと寄生インダクタンスLの共振となる。この周波数は、コンデンサの自己共振周波数ω_Cである。この自己共振周波数ω_CはωＬ＝1/ωＣとなる周波数であり、（２）式で示される。

Here, j is an imaginary unit, and ω is an angular frequency (rad / s). The angular frequency ω is 2π times the frequency f (Hz) (ω = 2πf).
Here, the term of 1 / jωC including the capacitance C becomes smaller as the used frequency (angular frequency ω) increases. Conversely, the term jωL including the parasitic inductance L becomes larger as the frequency increases. Therefore, when the frequency is low and ωL <1 / ωC, since the term relating to the capacitance C is large, the influence of the capacitance C is larger. Therefore, it operates as a capacitor C, that is, as a capacitor. However, as the frequency increases, the parasitic inductance term jωL becomes larger than the capacitance term 1 / jωC. Therefore, since the influence of the parasitic inductance becomes larger than the influence of the capacitance, it does not operate as a capacitor. When jωL = −1 / jωC, the capacitance C and the parasitic inductance cancel each other. At this frequency, the impedance Z _C is minimized and resonance of the capacitance C and the parasitic inductance L occurs. This frequency is the self-resonant frequency ω _C of the capacitor. This self-resonant frequency ω _C is a frequency at which ωL = 1 / ωC, and is expressed by the equation (2).

Therefore, conventionally, the usable band of the capacitor is limited by this series resonance. In order to cope with this point, an attempt has been made to expand the usable band of the capacitor by making two elements in one capacitor (for example, see Patent Document 1). In the capacitor proposed in Patent Document 1, another capacitor is formed in parallel on one plane of the parallel plate capacitor by the upper and lower electrodes, and the upper electrode is connected to the land on the substrate by wire bonding. Broadband characteristics are secured by using two types of series resonance of two capacitors.
JP 2001-143964 A

In the capacitor described in Patent Document 1 described above, since two capacitors are formed in one element, the element structure is complicated and large, resulting in a structure different from the conventional one, resulting in high costs. was there. In addition, wire bonding is used for mounting, which increases the number of assembly steps and increases the mounting area. Furthermore, in the method described in Patent Document 1, the series resonance frequency is not changed, and the capacitor becomes inductive in a band higher than the series resonance frequency, so that the band where the original function of the capacitor can be performed cannot be expanded. It was.
An object of the present invention is to solve the above-described problems of the prior art, and an object of the present invention is to provide a capacitor element having a wide usable band without complicating and increasing the element structure. It is to be.

In order to achieve the above object, according to the present invention, in a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes, the frequency at which the orientation polarization of the dielectric disappears is self-resonant. A capacitor element characterized by being set lower than the frequency is provided.
In order to achieve the above goal, according to the present invention, in a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes, the dielectric constant changes due to the disappearance of the orientation polarization of the dielectric. When the previous dielectric constant is ε _L , the relaxation time τ _C is such that the orientation polarization disappears at a frequency lower than the self-resonant frequency when the capacitor element is configured using a dielectric having a dielectric constant ε _L. There is provided a capacitor element characterized by using a dielectric having the same.

In order to achieve the above object, according to the present invention, in a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes, the capacitance of the capacitor element and the dielectric constant of the dielectric are The capacitor constant, which is the ratio, is k (m) (for example, the value obtained by length x width ÷ thickness when the influence at the edge is ignored for a parallel plate type capacitor), the parasitic inductance of the capacitor element is L, and the dielectric orientation When the dielectric constant of the dielectric at a frequency sufficiently lower than the frequency at which the polarization disappears is ε _L , the relaxation time τ _{C of the} dielectric is

を満たすことを特徴とするコンデンサ素子、が提供される。

The capacitor element characterized by satisfying the above is provided.

In order to achieve the above object, according to the present invention, there is provided a method for manufacturing a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes,
(1) a process of determining the shape of a capacitor element including electrodes and terminals;
(2) A process of obtaining a capacitor constant k, which is a ratio between the capacitance of the capacitor element and the dielectric constant of the capacitor, and a parasitic inductance L of the capacitor element from the determined shape of the capacitor element;
(3) a process of selecting a dielectric whose frequency at which the orientation polarization of the dielectric disappears is lower than a self-resonant frequency;
(4) a process of producing a capacitor element using the dielectric element selected in the previous process;
There is provided a method of manufacturing a capacitor element characterized by comprising:

In order to achieve the above object, according to the present invention, there is provided a method for manufacturing a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes,
(1) a process of determining the shape of a capacitor element including electrodes and terminals;
(2) A process of obtaining a capacitor constant k, which is a ratio between the capacitance of the capacitor element and the dielectric constant of the capacitor, and a parasitic inductance L of the capacitor element from the determined shape of the capacitor element;
(3) When the dielectric constant of the dielectric at a frequency sufficiently lower than the frequency at which the orientation polarization of the dielectric disappears is ε _L , the relaxation time τ _C is

を満たす誘電体を選定する過程と、
（４）前過程で選定された誘電体素子を用いてコンデンサ素子を作製する過程と、
を有することを特徴とするコンデンサ素子の製造方法、が提供される。

A process of selecting a dielectric that satisfies
(4) a process of producing a capacitor element using the dielectric element selected in the previous process;
There is provided a method of manufacturing a capacitor element characterized by comprising:

In order to achieve the above object, according to the present invention, there is provided a method for manufacturing a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes,
(1) a process of determining the shape of a capacitor element including electrodes and terminals;
(2) A process of obtaining a capacitor constant k, which is a ratio between the capacitance of the capacitor element and the dielectric constant of the capacitor, and a parasitic inductance L of the capacitor element from the determined shape of the capacitor element;
(3) When the dielectric constants of the dielectric at frequencies sufficiently lower and higher than the frequency at which the orientation polarization of the dielectric disappears are ε _L and ε _H respectively, the relaxation time τ _C is

を満たす誘電体を選定する過程と、
（４）前過程で選定された誘電体素子を用いてコンデンサ素子を作製する過程と、
を有することを特徴とするコンデンサ素子の製造方法、が提供される。
［作用］

A process of selecting a dielectric that satisfies
(4) a process of producing a capacitor element using the dielectric element selected in the previous process;
There is provided a method of manufacturing a capacitor element characterized by comprising:
[Action]

As described above, the equivalent impedance of the capacitor is given by the above equation (1). Since 1 / ωC> ωL below the resonance frequency, the impedance is capacitive and the capacitor can perform its original function. In the band exceeding the frequency, ωL> 1 / ωC and inductive impedance is obtained, so that the capacitor cannot perform its original function. Therefore, in order to widen the usable band as a capacitor, it is necessary to change the resonance frequency ω _C to the high frequency side.

Thus, as shown in the above equation (2), the self-resonant frequency can be shifted to a high frequency by reducing the capacitance C of the capacitor. However, at a low frequency, it is necessary to secure the capacitance C of the capacitor. Therefore, in the present invention, by utilizing the dielectric dispersion indicating the frequency dependence of the dielectric constant of the dielectric, the capacitance C is decreased at a high frequency while keeping the capacitance C at a low frequency, and the self-resonant frequency is increased to a high frequency. Make transitions.
The capacitance of the capacitor is proportional to the dielectric constant of the dielectric. Therefore, the capacitance of the capacitor is reduced at a high frequency by changing the dielectric constant of the dielectric according to the frequency. For this purpose, the phenomenon of dielectric dispersion is used. For example, as shown in Tadashi Shiogama, “Applied Technology of Insulating and Dielectric Ceramics”, CMC Publishing, August 18, 2003, pp.20-25, the polarization of dielectrics has a resonance type. There are polarization and relaxation-type polarization, and resonance-type polarization includes electronic polarization and ion polarization, and relaxation-type polarization includes orientation polarization and interface polarization. Since the orientation polarization and the interface polarization are relaxation types, the dielectric dispersion caused by these is also called dielectric relaxation.

Electron polarization is a phenomenon in which the center of an electron cloud is displaced with respect to the center of gravity of an atomic nucleus by applying an electric field, and is a phenomenon in the ultraviolet region. Ion polarization is polarization in which positive and negative ions are relatively displaced by an electric field, and is a phenomenon in the infrared region. Orientation polarization is polarization in which permanent dipoles are oriented by an electric field, and is a phenomenon in radio frequency. Interfacial polarization is polarization in which charges are accumulated at an interface by applying an electric field in a dielectric in which charged particles are unevenly distributed, and is a phenomenon at audio frequencies. Of these polarizations, the interfacial polarization can be ignored in uniform dielectrics and disappears in the high frequency band, so it can be ignored if the operation of the capacitor in the high frequency band is a problem. . Therefore, only the behavior of polarization other than interfacial polarization will be further described below. FIG. 1 is a diagram showing polarization as a function of frequency. Here, assuming that the polarization due to orientation polarization is Po, the polarization due to ion polarization is Pi, and the polarization due to electronic polarization is Pe, when an alternating electric field is applied to the dielectric, all the polarizations can follow the electric field change in the low frequency band. Therefore, the polarization P is Po + Pi + Pe. When the frequency exceeds a certain value (for example, 10 ⁹ Hz) in the high frequency band, the orientation polarization cannot follow the electric field change and disappears. Therefore, the polarization P becomes Pi + Pe, and the dielectric constant is greatly reduced. When the frequency is further increased, the ionic polarization disappears, the polarization P becomes only Pe, and the dielectric constant further decreases. When reaching the ultraviolet region, the electronic polarization disappears and the polarization P becomes zero.
A change in dielectric constant due to dielectric relaxation due to disappearance of orientational polarization is approximated by equation (3) (see, for example, the aforementioned book).

ここで、ε_Ｈ（Ｆ/ｍ）は誘電緩和が発生する周波数より十分高い周波数での誘電率、ε_Ｌ（Ｆ/ｍ）は誘電緩和が発生する周波数より十分低い周波数での誘電率、τは緩和時間（ｓ）（誘電緩和の時定数、誘電率の変化する速度）である。これらの値は、誘電体の材質によって決まる。（３）の式において、ωτが１に近い場合に誘電率の変化が大きい。したがって、角周波数ωが誘電緩和時間の逆数に近い値となる場合に誘電率が大きく変化する。つまり、誘電体は、ωτ≒１の周波数付近において誘電緩和により誘電率が周波数の上昇とともに大きく減少する。そのため、角周波数ω≒１/τとなる周波数付近において誘電率の減少に伴いコンデンサのキャパシタンスCも大きく減少する。

Here, ε _H (F / m) is a dielectric constant at a frequency sufficiently higher than the frequency at which dielectric relaxation occurs, ε _L (F / m) is a dielectric constant at a frequency sufficiently lower than the frequency at which dielectric relaxation occurs, τ Is relaxation time (s) (dielectric relaxation time constant, rate of change of dielectric constant). These values are determined by the material of the dielectric. In the equation (3), when ωτ is close to 1, the change in dielectric constant is large. Therefore, when the angular frequency ω becomes a value close to the reciprocal of the dielectric relaxation time, the dielectric constant changes greatly. That is, the dielectric constant of the dielectric decreases greatly with increasing frequency due to dielectric relaxation near the frequency of ωτ≈1. For this reason, the capacitance C of the capacitor is greatly reduced as the dielectric constant decreases in the vicinity of the frequency where the angular frequency ω≈1 / τ.

In the present invention, the material is adjusted so that dielectric relaxation of the dielectric occurs at a frequency lower than the self-resonant frequency of the capacitor. For example, when forming the dielectric, adjustment is made so that dielectric relaxation occurs at a frequency lower than the self-resonant frequency by mixing other substances or changing the sintering conditions of the dielectric. Thereby, at a frequency lower than the resonance frequency, a decrease in the dielectric constant occurs with an increase in frequency, and accordingly, the capacitance of the capacitor decreases. Since the resonance frequency is inversely proportional to the 1/2 power of the capacitance, if the capacitance decreases, the resonance frequency changes to a high frequency. Further, at a low frequency where the influence of dielectric relaxation does not occur, the dielectric constant is equivalent to that of a conventional capacitor, so that the operation at a low frequency does not change. Therefore, by setting the frequency at which the dielectric constant decreases due to dielectric relaxation to an appropriate value equal to or lower than the self-resonant frequency, the usable bandwidth of the capacitor increases.
Further, the capacitor of the present invention can be operated as a capacitor having a different capacitance depending on the frequency by using a phenomenon that the dielectric constant at a high frequency is lowered due to dielectric relaxation and the capacitance of the capacitor is reduced.

According to the present invention, since dielectric relaxation of the dielectric occurs at a frequency lower than the self-resonance frequency, the self-resonance frequency is determined by the capacitance reduced by the dielectric relaxation, and thus the self-resonance frequency can be increased. The usable frequency band of the capacitor can be widened. That is, in a capacitor used as a capacitive element, a range in which capacitive characteristics can be maintained up to a self-resonant frequency changed to a high frequency side is expanded, and a range that can be used as a low impedance element used for voltage stabilization is expanded.
In addition, the present invention does not achieve the broadband compatibility of the capacitor by making two capacitors in one element, so that the element structure is not complicated and the mounting area is not increased. In addition, the conventional method can be applied as it is to the manufacturing process, and a high-performance element can be provided at a low cost.

Next, embodiments of the present invention will be described in detail with reference to mathematical expressions and drawings.
When the dielectric polarization relaxation time is τ and the dielectric constant ωτ << 1, that is, the dielectric constant when polarization due to orientation polarization is ε _L , ωτ >> 1, that is, orientation polarization due to dielectric relaxation. When the dielectric constant after loss of polarization due to ε is ε _H , the change in the real part ε ′ of the complex dielectric constant due to dielectric relaxation of the dielectric is expressed by equation (3). Moreover, the change of the dielectric constant at this time is shown by a solid line in FIG. In the figure, ε ₀ is the dielectric constant of vacuum.

Since the capacitance of a capacitor is proportional to the dielectric constant of the dielectric, the capacitance in the low frequency range to be ωτ«1 is, C = kε _L, and the capacitance at the high-frequency region as a ωτ»1 includes a C = kε _H Become. In other words, the capacitance of the capacitor decreases from kε _L to kε _{H as the} frequency increases. Here, k is a constant determined by the size and shape of the capacitor, and is called a capacitor constant. The parasitic inductance L is also determined by the size and shape of the capacitor.
In the present invention, resonance is generated at a frequency equal to or higher than the frequency at which dielectric relaxation of the dielectric occurs. Therefore, the resonance frequency ω _CH is expressed by the equation (4).

On the other hand, assuming that resonance occurs at a frequency lower than the frequency at which dielectric relaxation occurs as in the case of the conventional example, the resonance frequency ω _CL is expressed by equation (5).

したがって、本発明のコンデンサ素子の共振周波数は、従来例の場合にくらべ√(ε_L/ε_Ｈ)倍になる。

Therefore, the resonance frequency of the capacitor element of the present invention is √ (ε _L / ε _H ) times as compared with the conventional example.

Further, even if the dielectric constant does not become ε _H , the resonant frequency can be shifted to a high frequency by adjusting τ so as to resonate in the vicinity where dielectric relaxation occurs, and the high frequency dielectric constant can be reduced. According to the equation (3), at a frequency where ωτ << 1, the dielectric constant does not decrease due to dielectric relaxation, but when ωτ approaches 1, the dielectric constant begins to decrease. Therefore, τ is adjusted so that the resonance frequency is higher than the frequency at which the dielectric constant of the dielectric decreases due to dielectric relaxation. Thereby, the resonance frequency transitions to a high frequency due to a decrease in the dielectric constant due to dielectric relaxation. Here, considering a frequency where ωτ <1/3, the dielectric constant ε ′ changes only about 10% of (ε _L −ε _H ). Since the transition of the resonance frequency is inversely proportional to the 1/2 power of the dielectric constant, the resonance frequency has a change of less than 5%, and there is no significant effect. Therefore, when resonating at a frequency equal to or lower than ωτ <1/3, the resonance frequency does not change much and the effect of using dielectric relaxation is less than that of a conventional capacitor in which resonance occurs at a frequency where ωτ << 1. . Therefore, when the resonance frequency ω _C and the relaxation time τ _C are set as ω _C τ _C ≧ 1/3 so that the resonance frequency is increased by 5% or more, that is, the dielectric constant ε ′ is decreased by 10% or more, τ _C ≧ 1 / (3ω _C ). Here, when ω _C is approximated by equation (5), τ _C satisfies equation (6).

したがって、誘電緩和を効果的に利用するためには、緩和時間は（６）式のように設定することが望ましい。これにより、共振点の誘電率ε′をε_Lより（ε_L−ε_Ｈ）の10％以上低い値に下げることができ、その分コンデンサ素子の使用可能範囲を広げることができる。

Therefore, in order to effectively use the dielectric relaxation, it is desirable to set the relaxation time as shown in equation (6). Thus, it is possible to reduce to a low value of 10% or more of the dielectric constant of the resonance point epsilon 'than _{ε L (ε L -ε H)} , it is possible to widen the usable range of the amount the capacitor element.

In addition, when τ is larger than a sufficient value, the capacitance at low frequencies is also reduced. If the capacitance of a capacitor at low frequency decreases, the function as a capacitor will be impaired. Therefore, in order to achieve high performance as a capacitor, the dielectric relaxation of the dielectric should be as low as possible. Is good.
In order to prevent the influence of dielectric relaxation of the dielectric material up to a high frequency, the relaxation time τ should be set so that the dielectric constant of the dielectric material is sufficiently reduced by the disappearance of orientation polarization at the self-resonant frequency. . That is, the relaxation time τ is not effective so that the orientation polarization disappears at a frequency lower than that. According to the present invention, it is effective to set the relaxation time τ so that the dielectric constant of the dielectric at the self-resonant frequency of the capacitor element sufficiently approaches the dielectric constant ε _H when the orientation polarization completely disappears. A relaxation time can be set.
Therefore, the second term on the right side of the equation (3) is dielectric so that resonance occurs at a frequency that does not become 1/1000 or less of (ε _L −ε _H ), that is, at a frequency that (1 + ω ² τ ² ) becomes 1000 or less. Select and adjust body. At this time, the resonance frequency ω _C and the relaxation time τ _C satisfy ω _C τ _C ≦ 31.6, and the relaxation time τ _C is τ _C ≦ 31.6 / ω _C , that is, τ _C ≦ 31.6√ (Lkε _C ). (Ε _C is the dielectric constant at the resonance frequency). Here, since the dielectric constant ε _C at the resonance frequency approximates ε _H , when ε _H is substituted into the above equation, the relaxation time τ _C of the dielectric is expressed by equation (7).

このように、ωτ≦31.6とすると、共振点での誘電率は、ε_Ｈとε_Lの差の1/1000程度にまで変化するが、これ以上τを大きくしても、共振周波数はほとんど高周波に遷移しない。そのため、共振周波数を高くしてコンデンサ素子の利用可能周波数範囲を最大限に拡大しつつ、低周波側の特性劣化を抑えることができる。
したがって、コンデンサの誘電体を、緩和時間τ_Cを（８）式を満たす値になる誘電体を選択、調整することで、コンデンサの自己共振周波数を高周波にシフトし、より広帯域で使用可能なコンデンサを実現できる。

Thus, if the .omega..tau ≦ 31.6, the dielectric constant at the resonance point, varies to about 1/1000 of the difference between the epsilon _H and epsilon _L, be increased any more tau, the resonance frequency is mostly high frequency Does not transition to Therefore, it is possible to suppress the characteristic deterioration on the low frequency side while increasing the resonance frequency to maximize the usable frequency range of the capacitor element.
Therefore, by selecting and adjusting the dielectric of the capacitor so that the relaxation time τ _C is a value satisfying the equation (8), the self-resonant frequency of the capacitor is shifted to a high frequency, and the capacitor can be used in a wider band. Can be realized.

FIG. 3 shows the result of simulation based on the equation (8). A 1 mm × 1 mm parallel plate type capacitor was simulated, the dielectric thickness was 1 μm, the parasitic inductance was L = 0.32 nH, and the relative dielectric constant (ε _L / ε ₀ ) was ε _rL = 9.2. FIG. 3 shows the characteristics of a conventional capacitor with a dotted line. The solid line shows the characteristics when a dielectric having a dielectric relaxation time of 1.6 ns _whose dielectric constant (ε _H / ε ₀ ) changes to ε _rH = 1.9 due to dielectric relaxation is used for this capacitor.
In the conventional capacitor characteristics, the resonance frequency occurs at 3.3 GHz, whereas in the capacitor element of the present invention, the resonance frequency changes to a high frequency up to 6.6 GHz. Therefore, in the element of the present invention, the usable band is widened to a high frequency twice that of the conventional capacitor.

Next, a method for manufacturing the capacitor element of the present invention will be described. When manufacturing a capacitor, such as an electrolytic capacitor, a film capacitor, or a ceramic capacitor, the structure is first determined. Thereafter, the constant k of the capacitor and the value L of the parasitic inductance are obtained by an electromagnetic field simulator or a sample prototype. Then, the dielectric constant is obtained from the capacitance to be realized by the capacitor.
Using the obtained values of k and L and the dielectric constant of the dielectric, an appropriate relaxation time τ is obtained according to equations (6) to (8). Based on the obtained relaxation time, a dielectric having an appropriate polarization relaxation time is selected and adjusted. A capacitor element using the dielectric relaxation of the present invention can be provided by manufacturing a capacitor using the selected and adjusted dielectric.

Next, another embodiment of the present invention will be described. In the present embodiment, the self-resonant frequency of the element is shifted from the frequency of ωτ = 1, and a dielectric having a relaxation time τ _{C at} which the increase in loss in dielectric relaxation is small at the self-resonant frequency is used. As a result, the influence of an increase in loss of dielectric relaxation is suppressed, and the usable frequency band is extended.
The reason will be explained. Near the self-resonant frequency, the impedance due to the capacitance component of the capacitor is small. Further, at a frequency of ωτ = 1, an increase in impedance due to loss increases due to an increase in loss due to dielectric relaxation. For this reason, when the self-resonant frequency of the capacitor is close to the frequency at which ωτ = 1, the impedance due to the capacitance component becomes smaller than the impedance due to loss. For this reason, the influence of the loss becomes stronger than the influence of the capacitance component, so that the operation as the capacitor element is impaired.
Therefore, by using a dielectric that has a relaxation time such that the dielectric loss at the self-resonant frequency at the dielectric constant after the dielectric constant is reduced due to the disappearance of the orientation polarization of the dielectric, the resonant frequency of the element And the frequency at which ωτ = 1 are shifted to reduce the influence of dielectric loss at the resonance frequency.

  Due to dielectric relaxation of the dielectric, the imaginary part of the complex dielectric constant, which is a loss of the dielectric, increases. The change in the imaginary part ε ″ of the complex permittivity due to the dielectric relaxation of the dielectric is expressed by the equation (9) (for example, see the above-mentioned book). The change with respect to the frequency is shown by a dotted line in FIG.

複素誘電率の虚部は、誘電体での損失を表すため、複素誘電率の虚部が最大となる点において、誘電体の損失が最大となる。したがって、ωτ=１の周波数で誘電体の損失が一番大きくなり、それ以上の周波数においては、減少する。誘電体の損失が特に重大となるのは、コンデンサの共振周波数付近においてである。それは、共振周波数付近において、コンデンサのインピーダンスＺ_Ｃが、キャパシタンス成分Cの影響と、寄生インダクタンス成分Lがそれぞれ打ち消しあって微小となるために、損失の影響が強くでるためである。逆に、共振周波数の周波数から外れると、キャパシタンス成分Cか寄生インダクタンス成分Lの影響が強くなるため、損失の影響は相対的に少なくなる。そのため、コンデンサの共振点において誘電体での損失の増加を回避することにより、複素誘電率虚部が増大する影響を少なくできる。

Since the imaginary part of the complex dielectric constant represents a loss in the dielectric, the loss of the dielectric is maximized at the point where the imaginary part of the complex dielectric constant is maximized. Therefore, the loss of the dielectric becomes the largest at a frequency of ωτ = 1, and decreases at a frequency higher than that. The loss of dielectric is particularly significant near the resonant frequency of the capacitor. Which in the vicinity of the resonance frequency, the impedance Z _C of the capacitor, the influence of the capacitance component C, and the parasitic inductance component L is cancel each other respectively small, because leaving strong influence of losses. On the other hand, when the frequency deviates from the resonance frequency, the influence of the capacitance component C or the parasitic inductance component L becomes strong, so the influence of the loss is relatively reduced. Therefore, by avoiding an increase in loss in the dielectric at the resonance point of the capacitor, the influence of increasing the imaginary part of the complex permittivity can be reduced.

In this embodiment, assuming that the dielectric is selected so that resonance occurs at a frequency ω _C at which the loss is reduced to 1/5 or less from the point at which the loss of the dielectric becomes maximum,
ε ″ (ω _C τ _C ) ≦ ε ″ (ωτ = 1) / 5
From equation (9)
ω _C τ _C / (1 + ω _C ² τ _C ² ) ≦ 1/10
Therefore, ω _C τ _C ≧ 10, that is, τ _C ≧ 10√ (Lkε _C ) is obtained (ε _C is the dielectric constant at the resonance frequency). Since the dielectric constant epsilon _C at the resonance point approximates epsilon _H, and substituting epsilon _H in the above equation is obtained (10).

誘電体の緩和時間τ_Ｃを（１０）式を満たすように設定することにより、誘電体の誘電緩和による損失の上昇による影響を抑えることができる。すなわち、（１０）式に示す値に緩和時間を設定した場合においては、共振周波数における複素誘電率虚部は、ωτ=1が共振点の場合と比較し、5分の1以下となっており、誘電損の影響を少なくできる。

By setting the relaxation time τ _C of the dielectric so as to satisfy the expression (10), it is possible to suppress the influence of the increase in loss due to the dielectric relaxation of the dielectric. That is, when the relaxation time is set to the value shown in the equation (10), the imaginary part of the complex permittivity at the resonance frequency is 1/5 or less compared to the case where ωτ = 1 is the resonance point. The influence of dielectric loss can be reduced.

In the present invention, the dielectric material used is not particularly limited. An organic material, an inorganic material, or a mixture thereof can be used as appropriate. For example, the capacitor can be formed of a dielectric made of a high molecular compound or a mixture thereof. As the dielectric, for example, a polymer compound in which dielectric dispersion occurs in a target frequency band and a mixture thereof among polymers such as resins such as polyphenylene sulfide, which has been used as a material for conventional film capacitors, can be used. As a result, it is expected that the conventional manufacturing equipment can be diverted and diverted with minimal modifications, and there is an industrial advantage. Further, any material that causes dielectric dispersion in the target frequency band can be used without being limited to the resin system. Furthermore, a dielectric in which at least one of the polymer compounds is an inorganic polymer compound can be used. By using an inorganic polymer compound, a capacitor having higher heat resistance than that of a resin or an organic polymer can be formed.
The case where an organic polymer compound is used as the dielectric will be described in further detail. Examples of the organic polymer compound include polypyrrole, polythiophene, and polyaniline. Since these or other organic polymer compounds have a large molecular weight and it is easy to adjust the molecular unit, the frequency at which dielectric dispersion occurs can be freely adjusted.

  Further, a metal oxide can be used as the dielectric. In particular, a perovskite type compound or a mixture thereof can be used as the metal oxide. Examples of the perovskite type compound include calcium copper titanate or a mixture thereof, a compound similar to titanate, and a mixture thereof. As a result, a dielectric element having a large dielectric constant can be used, and a capacitor element that functions effectively up to a high frequency can be realized by the effect of dielectric relaxation.

Next, an embodiment in which the present invention is applied to a ceramic capacitor will be described.
FIG. 4 is a perspective view of the ceramic capacitor according to the first embodiment. There is a dielectric 41 between the upper electrode 42 and the lower electrode 43 to form a capacitor. At this time, assuming that the thickness t of the dielectric is sufficiently smaller than the width w and the depth d and the influence of the edge of the dielectric is sufficiently small, the capacitor constant k is obtained by k = wd / t. It is done. Here, if the width w is 300 μm, the depth d is 300 μm, and the thickness t is 5 μm, k = 0.018.
When silicon carbide SiC is used for the dielectric 41, the relative dielectric constant ε _rL before dielectric relaxation is 99.9, and the relative dielectric constant ε _rH after dielectric relaxation is 13.1. Therefore, ε _L and ε _H are ε _L = 0.885 × 10 ⁻⁹ and εH = 0.116 × 10 ⁻⁹ , respectively, multiplied by the dielectric constant ε _{0 of} vacuum. At this time, when the parasitic inductance L was obtained by analysis using a three-dimensional electromagnetic simulator including the terminals 44 and 45 based on the dielectric constant before dielectric relaxation, it was 0.26 nH.

If these values are applied to the equation (8), the target relaxation time τ _C is 2.15 × 10 ^{−11 to} 7.36 × 10 ⁻¹⁰ . Here, the relaxation time τ _C can be adjusted to 6.48 × 10 ⁻¹⁰ by adding beryllium oxide when the silicon carbide SiC used for the dielectric 41 is sintered. Therefore, the configuration of the present invention can be implemented by using silicon carbide SiC to which beryllium oxide BeO is added as a dielectric. FIG. 5 shows the frequency characteristics of the impedance at this time. The resonance frequency is 6.83 GHz, which is 2.75 times the resonance frequency of 2.48 GHz when a capacitor having the same structure is formed using silicon carbide SiC to which beryllium oxide BeO is not added. Therefore, if the capacitor operating frequency range is up to the resonance frequency, the capacitor operating frequency range is expanded 2.75 times.

FIG. 6 is a perspective view of the ceramic capacitor according to the second embodiment. In Example 2, a ceramic capacitor having an outer dimension: width 2.0 mm × depth 1.25 mm × height 0.85 mm and a capacitance at a frequency before dielectric relaxation occurs: 220 nF, which is called 2012 size, is produced. As shown in FIG. 6, the first electrodes 62 and the second electrodes 63 are alternately arranged with the dielectric 61 interposed therebetween, and the first electrodes 62 are connected to the first terminals 64, and the second electrodes The electrode 63 is connected to the second terminal 65. The film thickness t of the dielectric 61 is 5 μm, and the effective dimensions of the electrode are as follows: the width w is 1.8 mm, the depth d is 1.0 mm, and the number of layers of the dielectric 61 is 70. Displayed). At this time, assuming that the thickness t of the dielectric is sufficiently smaller than the width w and the depth d and the influence of the edge of the dielectric is sufficiently small, the capacitor constant k is k = wd / t × 70 is 25.2. Here, when other ceramic capacitors having the same structure were measured, the parasitic inductance was 0.53 nH. In order to realize a capacitance of 220 nF with the capacitor having this structure, the dielectric constant of the dielectric before dielectric relaxation is about 1000. Here, assuming that the relative dielectric constant before dielectric relaxation of the dielectric is 1000, the minimum value of the relaxation time is obtained from the equation (8), which is about 3.6 × 10 ⁻⁹ . In order to produce a capacitor having the above capacitance, a dielectric 61 is obtained by using a mixture of calcium titanate copper CaCu ₃ Ti ₄ O ₁₂ and calcium titanate CaTiO ₃ synthesized from high-purity CaO ₃ , CuO, and TiO _2. The relative permittivity before relaxation was adjusted to about 1000, and the relaxation time was adjusted to 3.6 × 10 ⁻⁹ or more. In this mixture, the dielectric constant after dielectric relaxation was about 10, and the relaxation time was about 1 × 10 ⁻⁸ . Therefore, this mixture satisfies the condition of equation (8). A capacitor having a desired capacitance could be produced using a dielectric made of this mixture. FIG. 7 shows the frequency characteristics of the impedance at this time.

The graph explaining the dielectric dispersion of a dielectric material. The graph showing the change of the dielectric constant at the time of dielectric relaxation of a dielectric. The graph which shows the impedance characteristic of the capacitor | condenser element of this invention. The perspective view which shows the ceramic capacitor of Example 1 of this invention. The graph which shows the impedance characteristic of the ceramic capacitor of Example 1 of this invention. The perspective view which shows the ceramic capacitor of Example 2 of this invention. The graph which shows the impedance characteristic of the ceramic capacitor of Example 2 of this invention. An equivalent circuit diagram of a general capacitor element.

Explanation of symbols

41 Dielectric 42 Upper Electrode 43 Lower Electrode 44 Upper Electrode Terminal 45 Lower Electrode Terminal 61 Dielectric 62 First Electrode 63 Second Electrode 64 First Terminal 65 Second Terminal

Claims (7)

A capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes, wherein a frequency at which the orientation polarization of the dielectric disappears is set lower than a self-resonant frequency. . In a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes, k is a capacitor constant that is a ratio between the capacitance of the capacitor element and the dielectric constant of the dielectric, L is a parasitic inductance of the capacitor element, When the dielectric constant of the dielectric at a frequency sufficiently lower than the frequency at which the orientation polarization of the dielectric disappears is ε _L , the relaxation time τ _{C of the} dielectric is

A capacitor element characterized by satisfying In a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes, k is a capacitor constant that is a ratio between the capacitance of the capacitor element and the dielectric constant of the dielectric, L is a parasitic inductance of the capacitor element, When the dielectric constant of the dielectric at a frequency sufficiently higher than the frequency at which the orientation polarization of the dielectric disappears is ε _H , the relaxation time τ _{C of the} dielectric is

A capacitor element characterized by satisfying The capacitor constant, which is the ratio between the capacitance of the capacitor element and the dielectric constant of the dielectric, is k, the parasitic inductance of the capacitor element is L, and the dielectric constant of the dielectric at a frequency sufficiently higher than the frequency at which the orientation polarization of the dielectric disappears is ε _H When the dielectric relaxation time τ _C is

The capacitor element according to claim 1, wherein: A method of manufacturing a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes,
(1) a process of determining the shape of a capacitor element including electrodes and terminals;
(2) A process of obtaining a capacitor constant k, which is a ratio between the capacitance of the capacitor element and the dielectric constant of the capacitor, and a parasitic inductance L of the capacitor element from the determined shape of the capacitor element;
(3) a process of selecting a dielectric whose frequency at which the orientation polarization of the dielectric disappears is lower than a self-resonant frequency;
(4) a process of manufacturing a capacitor element using the dielectric selected in the previous process;
A method of manufacturing a capacitor element, comprising: A method of manufacturing a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes,
(1) a process of determining the shape of a capacitor element including electrodes and terminals;
(2) A process of obtaining a capacitor constant k, which is a ratio between the capacitance of the capacitor element and the dielectric constant of the capacitor, and a parasitic inductance L of the capacitor element from the determined shape of the capacitor element;
(3) When the dielectric constant of the dielectric at a frequency sufficiently lower than the frequency at which the orientation polarization of the dielectric disappears is ε _L , the relaxation time τ _C is

A process of selecting a dielectric that satisfies
(4) a process of manufacturing a capacitor element using the dielectric selected in the previous process;
A method of manufacturing a capacitor element, comprising: A method of manufacturing a capacitor element having a pair of electrodes and a dielectric sandwiched between the pair of electrodes,
(1) a process of determining the shape of a capacitor element including electrodes and terminals;
(2) A process of obtaining a capacitor constant k, which is a ratio between the capacitance of the capacitor element and the dielectric constant of the capacitor, and a parasitic inductance L of the capacitor element from the determined shape of the capacitor element;
(3) When the dielectric constants of the dielectrics at frequencies sufficiently lower and sufficiently higher than the frequency at which the orientation polarization of the dielectric disappears are ε _L and ε _H respectively, the relaxation time τ _C is

A process of selecting a dielectric that satisfies
(4) a process of manufacturing a capacitor element using the dielectric selected in the previous process;
A method of manufacturing a capacitor element, comprising:

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